Micro drives are low profile miniature hard disk drives for portable applications, such as personal digital assistants, cell phones, music players, camera, digital recorders, etc. A micro drive includes the basic components of a conventional hard disk drive, but is much smaller. More particularly it includes rotatable media, i.e., one or more hard disks, a hub on which the one or more disks are mounted, a spindle affixed to a base plate and about which the hub and media rotate, and an electric motor to effectuate rotation of the hub and media. The electric motor typically comprises a rotor and a stator. The rotor may comprise one or more permanent magnets positioned about the hub, and the stator may comprise a plurality of fixed electromagnets disposed in a circular pattern proximate the permanent magnets on the hub or rotor. Controlling current flow through the electromagnets causes the hub and media to rotate.
The stator generally includes a circular member or yoke. Generally, a plurality of teeth extend inwardly from the circular portion of the yoke and are wrapped with wire to form individual electromagnets. However, the teeth can either extend inwardly or outwardly, depending on whether the motor is an interior or exterior stator type, as will be appreciated by one of skill in the art. Typically, an interior stator is employed in a 2.5″ and larger disk drive, wherein smaller form-factor drives employ an exterior stator because there is sufficient radial space for the windings. The yoke and teeth are normally a laminate, constructed from a number of layers of conductive material, although they may be a single core instead of a laminate. Each tooth has a distal and proximate end. The proximate end of each tooth is connected to the circular portion of the yoke and the distal end is opposite the proximate end and adjacent the permanent magnets mounted on the hub. Normally, disk drives use three phase electric motors and, therefore, the number of teeth is a multiple of the number three, e.g. 6, 9, 12 or more. Every third tooth is electrically connected or wired together to form each of the three phases. As outlined herein, every third tooth is wired together to form a single phase (i.e. a 9 slot, 12 pole ABC winding is described), but one skilled in the art will appreciate that other windings are possible depending on the number of poles and the number of slots provided. Thus, three separate wires would be used to individually control each phase of the motor. Coordinating the current flow through the independent wires coiled about the teeth of each phase controls the rotation of the rotor/hub.
Micro drives often utilize in-hub motors, meaning the rotor and stator are positioned inside the hub, or under-hub motors, meaning the stator is positioned underneath the rotor, in order to reduce the height of the motor and thereby reduce the overall height profile of the drive. Another way to reduce height is to alter the windings forming the coils on the stator teeth, which is very applicable with respect to smaller disk drives that must employ an exterior stator motor as described above. Normally, each tooth has multiple layers of windings. The totality of windings on a tooth comprises a coil. Thus, the stator height comprises the height of each tooth, plus two times the coil thickness. The height of each tooth comprises the plurality of conductive laminate layers forming each tooth, also referred to as the core of the electromagnet or a stator core. To alter the stator height, the diameter of the wire may be changed, the number of layers of windings may be changed and/or the height of the core may be changed.
The stator wires that form each coil generally enter and exit the coil at the proximate end of each tooth. This is because, as noted previously, the wires necessarily skip or cross over adjacent teeth in order to be wound in multiple phases. As should be appreciated, routing wires from the distal end of one tooth, either to the distal or proximate end of another tooth, while skipping over two intervening teeth, can cause problems. For example, the cross over wire(s) can interfere with the rotation of the hub, waste valuable space, and pose reliability and noise issues. Thus, in order to avoid interference with the hub, a stator coil will most always have an even number of winding layers in order for the wire to exit the tooth at the proximate end and not cross over any intervening coils. For example, the first layer is formed from the proximate end to the distal end of a tooth and the second layer of the winding is formed from the distal end to the proximate end. The wire will then be routed around the yoke perimeter to the next tooth that is in phase with the previously wound coil. Of course, there may be four or six or more winding layers and not just two. In this way, the wire does not interfere with the rotation of the rotor and, as noted, there will always be an even number of winding layers.
Another drawback of prior art cross-over wire interconnection schemes is that they compel the use of additional hardware. For example, some prior art stators include routing or retainer tabs interconnected to or interleaved within the layers of the stator yoke. The retainer tabs or hooks provide a location around the yoke for engaging and retaining the cross-over wires. This is an acceptable way to retain the cross-over wires in a predetermined location, however, additional complexity is added to the spindle motor which increases costs. Moreover, positioning the retaining tabs on the stator yoke, typically between adjacent teeth, promotes and reinforces the disadvantage that the start and finish of each stator coil still must be located at the proximate end of each tooth near the stator yoke thereby compelling an even number of coil winding layers.
While exiting wires at the proximate end of each stator tooth may simplify the routing of cross-over wires, it can also create other, unrelated limitations. As should be appreciated, to optimally design a disk drive the electric motor should also be optimized. This includes optimizing the characteristics of the stator. In the particular circumstances of a particular motor used in a particular design, it is not always desired simply to maximize the number of windings. For example, it may be desired to increase or decrease the number of laminate layers comprising each stator core, or to utilize an odd number of layers of windings rather than an even number, depending upon the wire diameter or gauge preferably selected for use in the drive. Changing one of these parameters can require changes to one or more of the others to maintain an optimized design. Thus, for small form factor electronic devices, the motor design must accommodate these factors while simultaneously seeking to decrease the height of the motor. Nonetheless, as noted above, in current drives it is more likely that the stator cores will have an even number of winding layers to avoid the problems created by cross-over wiring. As a result, it may not be possible both to optimize the motor and decrease its height. Trade offs may need to be made, such as sacrificing optimum performance to meet height restrictions caused by the number of layers of windings and/or the number of laminate layers, or sacrificing height to meet motor design objectives. The coil may have one less winding layer or one more winding layer than desired. If an additional winding is used, the stator height, and the overall drive height, will increase. If one less layer of windings is used, performance may be negatively affected, as might also be the case with an additional layer, and internal space may be unused and wasted.
Thus, it is a long felt need in the field of micro-drive production to provide a system that allows for an improved cross-over wire retainment strategy thereby providing the ability to decrease the height or thickness of the micro-drive while optimizing the characteristics of the motor for a particular end use application of the disk drive. The following disclosure describes an improved method of routing the cross-over wires between stator teeth that includes the addition of retaining tabs integrated into the base plate of the housing.